Deceleration of high-energy matrix-assisted laser desorption/ionization ions in an open cell for Fourier transform ion cyclotron resonance mass spectrometry.

A new method of ion deceleration in a Fourier transform ion cyclotron resonance (FTICR) open cell is described that improves the performance of FTICR-MS instruments equipped with an internal source for laser desorption/ionization. Ion deceleration occurs in the front trapping cylinder of an open cylindrical cell. Decelerating voltages up to 100 V can be applied for 10-500 micros to the front cylinder during ion introduction. The deceleration field is uniformly distributed along the cylinder length giving a "smooth" deceleration, which means that the deceleration is effective over a large time interval and a large m/z range. This results in improved trapping efficiency of high-energy ions. We demonstrate efficient trapping of high (m/z 66 kDa) mass ions and the possibility to reduce the width of the kinetic energy distribution of MALDI ions with this arrangement.